Aerial survey

ABSTRACT

Target positioning apparatus for use in aerial surveying has a viewing device and a laser alignment device for respectively approximately and accurately positioning a helicopter above a predetermined point on a terrain, and a height measuring device and horizontal distance measuring equipment which are automatically operated by the laser beam.

UnIted States Patent 11 1 1111 3,765,766 McConnell et al. Oct. 16, 1973[5 AERIAL SURVEY 3,523,660 s/1970 Atteberry et al. 244/1711 3,370,2932/l968 Green 250/203 R [76] mentors: Fmdemk Mccmnel" Bria 3,439,1704/1969 Zagone et al. 356/152 George f i 108 3,426,146 2/1969 Seaman356/152 Brow Cres, N- -;Ne1l J- 2,817,994 12/1957 Ehrenhaft et al.356/150 A t 5428 B D flfi j giggig r FOREIGN PATENTS OR APPLICATIONSCanada 854,266 ll/l952 Germany 33/] T [22] Filed: Aug. 30, 1972 OTHERPUBLICATIONS [211 Appl' 284,971 Geodolite 3A, Spectra-Physics, Inc.,Brochure,

3-1968. Related US. Application Data [60] Division of Ser. No. 65,259,Aug. 19, 1970, Pat. No. Primary Examiner-Samuel Feinberg 3,709,607,which is a continuation of Ser. No. Assistant s Buczinski 817,448, April18, 1969, abandoned. Attorney spencer & Kaye [52] US. Cl 356/4, 178/68,356/152,

250/203 R, 244/1711 [57] ABSTRACT [51] Int. Cl. G0lb 11/26 Targetpositioning apparatus for us in aerial survey- [58] Field of Search356/4, 5, 141, 152, g as a i wi g d v e and a laser alignment device356/172, 138; 250/203 R, 215; 244/17.11, for respectively approximatelyand accurately posi- 17,17; 33/1 T tioning a helicopter above apredetermined point on a terrain, and a height measuring device andhorizontal [56] Refere Cit d distance measuring equipment which areautomati- UNITED STATES PATENTS cally operated by the laser beam.

3,603,688 9/ 1 971 Smith-Vaniz 356/152 10 Claims, 3 Drawing Figures/$/GHT L/GHT 20 f0 /4 mums 505 AERIAL SURVEY CROSS REFERENCE TO RELATEDAPPLICATION This application is a division of application Ser. No.65,259, filed Aug. 19, 1970, now U.S. Pat. No. 3,709,607 which itself isa continuation of Ser. No. 817,448, filed April l8, 1969, and nowabandoned.

This invention relates to target positioning apparatus and methods foruse in aerial surveying.

Surveying has for many years been one of the most important aspects ofmining, petroleum or other field operation, and it is a time-consumingprocedure. All surveys rest primarily on linear measurements for thedirect determination of distances. In non-wooded, accessible areas,surveying has historically been carried out by surveyors using transitsand stadia poles. Often the system of surveying known as triangulation(which utilizes the simple geometrical princple that if one side and twoangles of a triangle are known, the measurements of the rest of thetriangle can be computed) is used. Thus, linear measurements may besupplemented by angular measurements. This enables distances to bedetermined over areas which cannot be measured directly, as, forexample, hilly or broken ground.

In wooded areas and in relatively inaccessible areas, both distance andangle measuring devices (transits and theodolites) placed at groundlevel cannot be used. Accordingly, it has been the practice to build atower on top of which sits a slave or master station, thus giving a lineof signt above the treetops for 20 to 30 miles distance. A portablesteel observation tower, as for example that known under the trade nameBilby Tower, has frequently been used. Such an observation tower is likea giant tripod, extensible to over 100 feet, and is provided with aninner tripod which holds the transit or theodolite, but does not vibrateat the movements of the surveyors who stand on the separate outer tower.The task of building or erecting such towers in remote areas has beenfacilitated in recent years by the use of helicopters, which cantransport both the men and the materials.

However, the building or erecting of such towers is an expensive andtime-consuming task. Consequently it has been suggested that thehelicopter could be used as a sighting target, if it could hoveraccurately over a point on the terrain. The practical success of such aproposal depends upon: firstly, the provision of accurate means ofmeasuring the distance from a fixed point (in line of signt with anddistant from the helicopter) to the helicopter; secondly, the provisionof sufficient hovering accuracy for the helicopter; and thirdly, theprovision of a satisfactory hover sight.

The first problem has been solved by use of a tellurometer, which is adistance measuring device utilizing line-of-sight radio waves. It is, ineffect, a two-way radio telephone system which operates between a masterunit and a remote unit. The second problem has been solved by provision,in the helicopter, of a stability augmentation system which allows for amore accurate hovering technique.

it has been suggested to solve the third problem and also to provide anaccurate surveying system and technique that the following procedure beutilized. A helicopter is fitted with a vertical rod (like a stadiapole) located at the centre of the top of the helicopter. Also installedin the helicopter and precisely located in the centre bottom of themachine is a plumb bob on a string, attached to a drum mechanism, formeasuring the distance of the helicopter above the ground. By lookingthrough a series of mirrors located in the pilot s compartment of thehelicopter, the pilot can see the string and plumb bob and a stationmark below him. The pilot can raise or lower the helicopter toaccommodate the height of the trees. He can also manoeuvre until theextended plumb bob is located exactly over the station mark. He can thenattempt to hold the helicopter in this fixed position while anothermember of the survey crew, using a tellurometer, takes a reading on thevertical pole attached to the top of the helicopter. The helicopter mayalso have attached to the top thereof a Grimes beacon or a strobe light,in-order that the general direction could be determined by thetellurometer operator in the distance. The height of the helicopter ismeasured by calibrating the plumb bob string. The pilot and thetellurometer operator are in radio contact so that the pilot can informthe operator when the plumb bob is precisely over the station mark in aposition for a reading to be taken.

While this system and procedure has proven fairly accurate, it is quiteexpensive. Furthermore, the accuracy is impaired by the fact that windandturbulence created by the helicopter may have an effect on thestability of the plumb bob line. Consequently, the stadia pole atop thehelicopter may not be along a line exactly ver- I tical to the stationmark.

It is an object of one aspect of this invention to pro} 4 vide anaccurate and economically feasible system for aerial surveying. Anobject of another aspect of this in vention is the provision of anaccurate and economically feasible procedure for aerial surveying.

In addition, it is an object of another aspect of this in-j vention toprovide a control and actuating mechanism which can aid in the operationof surveying equipment,

and contribute to an accurate and feasible system for' aerial surveying.I v By one aspect of this invention there is provided a" targetpositioning apparatus adapted to aid in the slut vey location of apredetermined point therebeneatliQ The target positioning apparatuscomprises a helicopter, means mounted on the helicopter enabling thepilot thereof to view the terrain beneath the helicopter when it isairborne, and a laser alignment means for indicating when the helicopteris positioned vertically over the point whose location it is desired tofix by survey and a distance measuring device for measuring thehorizontal position and for height of the helicopter. The hover sightpreferably includes a laser capable of projecting a laser beam directedvertically between the helicopter v and the point to be located.Additionally, a closedcircuit television system mounted on thehelicopter may be provided; the camera being directed to scan the iterrain beneath the helicopter when it is airborne and the viewingscreen being positioned such that it can be seen by the pilot thereof.

Another aspect of this invention relates to a method of surveying thelocation of a predetermined .point whose position it is desired todetermine at a giventime. A helicopter hovers generally above the point.

The next step is the projection of a laser beam vertically between thehelicopter and the point. The 'helico'pter is then positioned accuratelyover the point by reference to the laser beam, and survey measurements 7then are taken.

In accordance with the preferred practice of the present invention, aclosed-circuit television system is provided on the helicopter whichaids the pilot in seeing beneath the aircraft and in locating over thepoint on which it is desired to obtain a fix, and a laser beam directedvertically between the helicopter and the station mark is utilized as ahover sight to indicate when the aircraft is positioned vertically overthe point to be located. In one embodiment of the invention the laserbeam is projected vertically upward from the terrain beneath thehelicopter and a laser beam detector mounted on the helicopter informsthe pilot when he is accurately over the mark; optionally, the laserdetector may be utilized to trigger the operation of automatic distancemeasuring equipment.

It has been found advantageous in some circumstances to utilize aclosed-circuit television system in which the camera is mounted in thehelicopter by means of well-lubricated gimbal rings such that the camerais free to maintain an attitude substantially vertical to the earth whenthe helicopter is airborne. Also, the television console with viewingscreen is best located adjacent the instrument panel of the helicopterwhere it can be seen easily by the pilot. In such practice of thisinvention, the laser may be mounted on the television camera which iskept vertical to the earth; the laser projecting a beam onto the terrainfor viewing from the helicopter. Alternatively, as mentioned in thepreceding paragraph, the laser can be positioned over the point in sucha manner as to project a laser beam vertically upward from the point. Alaser beam detector mounted on the helicopter indicates when thehelicopter is accurately positioned over the point.

Another feature of the invention is the provision of a control andactuating mechanism responsive to the detection of a laser beam, whichmechanism can be utilized to aid in the operation of survey apparatusand in the accurate positioning of the helicopter over the point.

In order to take the desired survey may be for example, horizontaldistance measuring equipment such as autotape or tellurometer positionfixing devices. Further there is usually a the height measuring devicealso associated with the helicopter which is capable of accuratelydetermining the distance between the hovering helicopter and the pointmay be, for example, a calibrated, spring-loaded plumb bob and reel.

If desired, the laser beam detector can be utilized to activate certainpreselected mechanisms associated with the helicopter upon detection ofthe laser beam projected vertically upward. It can be used, for example,to automatically activate the horizontal distance measuring equipment.The detector can comprise plural detection cells, at least one such cellindicating that the helicopter is positioned accurately over the point,and at least another of the cells indicating when the helicopter hasdrifted such that it is not positioned over the point. The differentcells can be used to activate and positively deactive the distance andheight measuring device. The plural cells of the laser beam detector canbe arranged in the form of two concentric rings of cells in order tooperate as outlined above.

Therefore, the present invention provides a control and actuatingmechanism which is particularly suited to use in survey work, althoughit can find application in other situations wherein a laser beam isutilized and reference is made thereto for actuation and control ofother equipment. The mechanism includes a laser beam receiver with firstmeans for sensing a predetermined desired condition and in response tothe presence of that condition for initiating operation of a preselectedmechanism, and second means for sensing a predetermined undesiredcondition and in response thereto discontinuing operation of apreselected mechanism. In a preferred embodiment, the control andactuating mechanism utilizes a laser beam detector having pluraldetection cells. A first cell upon sensing the presence of a desiredcondition initiates operation of a preselected mechanism. A second cellupon sensing the presence of a predetermined undesirable conditionpositively discontinues operation of a preselected mechanism.

As an example, if the control and actuating mechanism is mounted in ahelicopter for use in survey work, the desired condition can be met whenthe hovering helicopter is accurately positioned vertically above apoint on the terrain, and the undesired condition may be achieved whenthe helicopter is no longer accurately positioned over that point.Consequently, when the first means in the laser beam receiver, i.e. afirst detection cell, senses the laser beam and that therefore thehelicopter is accurately positioned over the survey point, the distancemeasuring devices and the Grimes beacon or strobe light can be activatedand their operation commenced. When the second means in the laser beamreceiver, i.e. the second detection cell, senses that the helicopter hasdrifted, i.e. is no longer accurately positioned over the station mark,the operation of the distance measuring devices and the Grimes beacon orstrobe light can be terminated.

Another example of the actuation of a preselected mechanism would be therelease of the plumb bob reel mechanism when the helicopter isaccurately positioned over the survey point, so that the perpendiculardistance of the helicopter over the survey point at that time can bemeasured.

In the preferred procedure aspect of this invention, the method ofsurveying the location of a predetermined point comprises the steps of:(1) providing a helicopter equipped with a laser beam detector on theunderside and hovering generally above the point, (2) projecting a laserbeam vertically upward from a laser located directly over the point, (3)detecting when said helicopter is positioned accurately over the pointby reference to the laser beam detector, and (4) taking surveymeasurements when the helicopter is so positioned.

The helicopter which is used in the system and procedure of aspects ofthis invention preferably is one which is equipped with a stabilityaugmentation system, which aids in a more accurate hovering techniquethan may be otherwise possible. One such helicopter is known under thetrade name Hiller model SL4, and is manufactured by the l-lillerHelicopter Company. Another such helicopter is the Bell 47 model 38-]helicopter.

The laser can be attached to any normal instrument, and in the presentinvention, it is a portable laser preferably of the type known as atransit-laser. The inherent characteristics of a laser, namely theemission of an intense beam of coherent light (red in colour in a rubylaser) which is clearly visible either at night or in daylight, are usedto advantage. Since the laser beam remains essentially parallel and doesnot expand as it travels over long distances, the laser beam isanalogous to an endless, weightless, stretched string which is visibleover a great distance. it becomes, in effect, a clearly visiblereference line.

A transit-laser beam is clearly visible on a target one thousand feetaway as a spot whose centre can be judged to within about one-half inch.Simple detectors (for example goggles) are available, which by filteringout extraneous light in effect permit greater viewing range. Inaddition, the operator may use a retroreflector which will pick up thebeam at a substantial range allowing the operator to know whether or nothe is constantly on target. Should his instrument be jarred for anyreason, the retroreflector will make him aware that such has happened.At night, the transit-laser beam is visible for a distance of up toabout ten miles. One commercially available laser which may be used inthe practice of this invention is known as the University LaboratoriesModel 610 transit-laser.

The means associated with the helicopter for the taking of distancemeasurements may be simple or sophisticated. One such simple means is asight light by which transit readings may be taken from two knownlocations. Alternatively an autotape or a position-fixing device such asthe model MRB3 of Tellurometer Canada Limited may be used; these devicescan be adapted to be activated electronically by a laser detector. Uponreception of the laser beam, the laser detector then activates theautotape or the MRB3 which automatically takes distance readings onremote units located at known locations.

The closed-circuit television system which can be used in the variousaspects of this invention preferably is one which has high resolution,even under the conditions of vibration and other problems associatedwith helicopter operation, in order to provide a clear picture. One suchcommercially available system is manufactured under the brand name ofSony closed circuit television set.

The camera of the closed circuit television system in one embodiment maybe mounted pointing down and ahead through the tail boom of thehelicopter. The viewing console of the television system normally isplaced in front of the rudder pedals of the helicopter and is used bythe pilot to enable him to face his instrument panel and still be ableto see underneath his machine, thus facilitating his hovering over afixed point. The closed circuit television system enables the helicopterto hover over a station mark and to obtain a fix" over such stationmark. in another embodiment, the television camera preferably is mountedon welllubricated and ball-bearinged gimbal rings. Thus, re-

gardless of the attitude of the helicopter, the camera is free to moveso that it is perpendicular with the ground at all times when thehelicopter is airborne.

In a preferred embodiment of the present invention, a laser beamdetector is mounted on the helicopter, a good position being in front ofthe vertically directed television camera lens. The laser detector may,for example, be a single cell, or preferably may consist of twoconcentric rows of laser beam sensitive cells. These rows of cells canbe used to activate preselected mechanisms mounted on the helicopterupon reception of the beam from the laser mounted over the station markbelow.

In a second embodiment of this invention, the laser can be mounted onthe helicopter so that the laser beam is centrally located in line withthe sighting mechanisms on the helicopter and is always pointingvertically downward. in this way the pilot can see, by means of theclosed circuit television set, the positioning of the helicopter byobserving the laser beam with respect to the station mark on the groundbelow.

It is an additional advantage in the practice of this invention that atape recording of the television operations can be made and preserved.This tape recording could be reviewed later, after the field work iscompleted, should -.it be necessary to check the survey results.

The laser beam is used to provide an accurate positioning of thehovering helicopter over astation mark. The accurate measurement of thehelicoper "height would normally be carried out by using a plumb bobstring attached to a calibrated drum. When the plumb bob touches thestation mark, the exact height above the station mark can be read.

It is to be observed that reference has been made to a station mark.Other well-known survey points, such as bench marks, triangulationstation marks, traverse station marks and corner monuments, azimuthmarks, etc. are also interchangeable with station marks, and indeed, anypoint whose position it is desired to fix at a given time may bedesignated as a station mark."

Reference now will be made to the accompanying drawings which willillustrate the practice of the invention according to one embodimentthereof:

FIG. 1 is a schematic view of a helicopter hoveringover a station markundertaking survey work'from the air.

FIG. 2 is a view in more detail of the instrumentation utilized in thesurveymethod shown in FIG. 1; and

FIG. 3 is a schematic electrical diagram of .the control and actuatingmechanism and associated instrumentation, utilized in the practice ofthis invention in conjunction with the equipment illustrated in FIG. 2.FIG. 1 shows a hovering helicopter 10 which may be a Bell 47 model 3B1helicopter) hovering over a station mark 11, namely a point whoseposition it is desired to locate. The helicopter is provided with aheight measuring device 12, which in the embodiment shown'includes aplumb line 13 and a plumb bob l4. Alternatively, although not shown, thehelicopter may be provided with a stadia rod incorporated in the bottomthereof which can be read through a telescope on the ground to obtainthe measure of the vertical height of the helicopter above the stationmark. The helicopter is provided with a laser detector 16 mounted on theleft cargo rack. The detector 16 is adapted to receive the laser beamprojected by a laser 25 situated over bench mark 11. Directly above thedetector 16 is the lens'of a television camera 17, the screen 19 ofwhich is mounted adjacent the helicoper instrument panel 18;

Directly above the television camera 17 is a sight light 20, which maybe a Grimes beacon or a strobelite. This equipment is used to locate thepoint at station mark 11 in the horizontal plane. As seen more clearlyin FIG. 2, the altitude measuring device 12 includes a plumb bob 14 andreel 30, the reel being calibrated and spring loaded, and provided witha weight sensitive indicator. The spring release in the system recordsthe instant that plumb bob 14' touches the terrain, thus giving thevertical height of the calibrated drum 30 above the station mark 11.

Over station mark 11 is a tripod'2l, on the bench 22 of which is mounteda level 23, a vertical telescope 24,

and a transit-laser 25. The laser detector 16 includes a dome 26provided with two internal concentric rows of laser beam sensitive cells27 and 28, which may be photovoltaic or photoresistance cells. The lens29 of television camera 17 is in direct vertical line with the laserdetector 16. The instrument panel is also provided with indicator lights31 to be more fully described with reference to FIG. 3.

While not shown survey method FIG. 2, the rows 27 and 28 of laser beamsensitive cells may be coupled to the sight light and to the electronicdistance measuring equipment, e.g., an autotape or position fixingdevice known as model MRB3 of Tellurometer Canada Limited. The measuringmeans could be activated when the detector 16 receives the beam of thelaser 25; thus automatic distance readings may be taken on two remoteunits, one located at each of two known locations.

FIG. 3 schematically illustrates the electrical circuit diagram. A powersupply 32 is operatively connected to the dome 26 of the laser detector,to an on/off switch 33 and thence to a distance measuring device 37, tothe sight light 20, and to the sight light indicator light 34. The powersupply is also connected to the motor of the calibrated drum 30, whichis in turn connected to two indicator lights 35 and 36 on the instrumentpanel. The dome 26 of the laser receiver 16 is also connected to on/offswitch 33.

In operation, the pilot positions himself utilizing the closed circuittelevision system. The viewing console with screen 19 is mountedadjacent the instrument panel for easy line-of-vision requiring aminimum of eye movement by the pilot from the RPM indicator. it ispreferred that cross-hairs be placed on the console face to assist thepilot in positioning the helicopter over the station mark 11. Two-wayradio communication between the pilot and a man on the ground may alsobe used as an alternative positioning method.

As the helicopter manoeuvres over the survey point the dome 26 receivesthe laser beam from laser 25, and the beam will first fall on at leastone of the outer row of detection cells 27. This will produce no changesince the switch 33 will already be in the off position. When the laserbeam is detected by one of the inner row of cells 28, indicating thatthe helicopter is positioned vertically above the beam of laser 25,switch 33 closes and sight light 20, indicator light 34, and distancemeasuring equipment 37 will be turned on. If the helicopter drifts" offfrom the vertical, one of the outer row of detection cells 27 will betriggered opening switch 33 and positively discontinuing operation ofequipment 37 and lights 20 and 34. The turning on and off of switch 33in response to signals generated by the detection cells can be used toinitiate and terminate indicator lights, a sight light, and horizontaland vertical distance measuring equipment.

indicator light 35 may be a green light and indicator light 36 a redlight. They are controlled by a tension spring in the line 13, with thegreen light 35 being on until the plumb bob 14 touches the ground, atwhich time the green light 35 goes out and the red light 36 comes on.These two lights are in the pilots line of sight, either on thehelicopter instrument panel or on top of the television viewing console.These lights optionally could be eliminated or verified by the use of atwo-way radio on the occasions where a man is stationed on the ground bythe station mark.

We claim:

1. Target positioning apparatus for use in aerial surveying comprising ahelicopter, means mounted on said helicopter enabling the pilot thereofto view the terrain beneath the helicopter when it is airborne, andlaser alignment means for indicating when said helicopter is positionedvertically over a point on the terrain whose location it is desired tofix by survey, said laser alignment means including a laser capable ofprojecting a laser beam directed vertically between said helicopter andsaid point, a laser detector for detecting the laser beam, one of saidlaser and said laser detector being mounted on said helicopter, meansfor indicating to the pilot when the laser beam is aligned with saidlaser detector, and a distance measuring apparatus associated with saidhelicopter capable of determining the distance between the helicopterand said point.

2. Target positioning apparatus as defined in claim 1 wherein said laserdetector is mounted on said helicopter, and further comprising electriccircuit means connected to said laser detector for providing an outputsignal in response to alignment of the laser beam with said laserdetector, said distance measuring apparatus comprising horizontaldistance measuring apparatus operable in response to the output signalof said electric circuit means.

3. Target positioning apparatus as claimed in claim 2, wherein saidlaser detector comprises first and second laser sensing cell meansresponsive to said laser beam for providing first and second signals,respectively, controlling said electric circuit means, said electriccircuit means including means for initiating and discontinuing operationof said distance measuring device in response to said first and secondsignals, respectively.

4. Target positioning apparatus as claimed in claim 1, wherein saidlaser detector is mounted on saidhelicopter, and further comprisingelectric circuit means connected to said laser detector for providing anoutput signal in response to alignment of the laser beam with said laserdetector, said distance measuring device comprising a height measuringdevice operable in response to said output signal for measuring thedistance of said helicopter above said point.

5. Target positioning apparatus as claimed in claim 4, wherein saidlaser detector comprises first and second laser sensing cell meansresponsive to said laser beam for providing first and second signals,respectively, controlling said electric circuit means, said electriccircuit means including means for initiating and discontinuing operationof said distance measuring device in response to said first and secondsignals, respectively.

6. Target positioning apparatus as claimed in claim 2, wherein saiddistance measuring aparatus comprises a height measuring device formeasuring the distance of said helicopter above said point.

7. A method of surveying the location of a predetermined point on aterrain, which comprises the steps of viewing the terrain below thehelicopter and to facilitate manoeuvering of the helicopter into aposition generally above said point, projecting a laser beam verticallybetween said helicopter and said point, positioning said helicopteraccurately over said point by reference to said laser beam, and takingsurvey measurements while said helicopter is accurately positioned oversaid point.

8. A method as defined in claim 7 wherein said laser beam is projectedvertically downward from said helicopter, and said helicopter ispositioned accurately 10 said point.

10. A method as claimed in claim 9, which includes subsequentlydiscontinuing operation of the distance measuring equipment by usingsaid laser detector to sense when said helicopter has moved from oversaid point.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 765766 Dated October 16th 1973 Inventods) Frederick C. McConnell, GeorgeJason and Neil J.

Armstrong It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, after line 7, insert:

[73] Assignee: Spartan Air Services Limited, Ottawa,

Ontario, Canada-. Column 1, line 18, change "princple" to -principle--line 30,

change "signt" to -sight--; line 49, change "signt" to --sight Column 2,line 46, delete "and a". Column 3, line 43, delete "there is usually a";same line, delete "also"; line 44, delete "associated"; Column 6, line14, change "helicoper" to -helicopter-; line 33, change "surveymethod to-survey method--; line 54, change "helicoper" to --helicopter--.

Column 7, line 9, change "survey method" to -in-. Column 8, line 52,change "aparatus" to apparatus.

signed and sealed this 23rd day of April 19714..

(SEAL) Attest: I

EDWAFD M.FLETGI IER,JR. C. MARSHALL DANN Attesting Officer Commissionerof Patents F ORM PO-105O (10-69) USCOMM-DC OO376-P69 U.S. GOVERNMENTPRINTING OFFICE I909 O-SBB-EJI,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTEON Patent No.3,765,766 Dated ct b r 16th, 1973 lnventofls) Frederick C. McConnellGeorge Jason and Neil J.

Armstrong It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, after line 7, insert:

-- [73] Assignee: Spartan Air Services Limited, Ottawa,

Ontario, Canada.

Column 1, line 18, change "princple" to principle-- line 30,

change "signt" to sight-; line 49, change "signt" to sight- Column 2,line 46, delete "and a". Column 3, line 43, delete "there is usually a";same line, delete "also"; line 44, delete "associated"; Column 6, line14, change "helicoper" to -helicopter--; line 33, change "surveymethodto survey method-; line 54, change "helicoper" to --helicopter-.

Column 7, line 9, change "survey method" to in. Column 8, line 52,change "aparatus" to apparatus-.

Signed and sealed this 23rd day of April 19714..

(SEAL) Attest:

EDWARD I-I.FLETCHER,JR. C. MARSHALL DANN Attesting Officer Commissionerof Patents F ORM PO-105O (IO-69) USCOMM-DC 603764 69 h vs. GOVERNMENTPRINTING ornc: Ion 0-300-354.

1. Target positioning apparatus for use in aerial surveying comprising ahelicopter, means mounted on said helicopter enabling the pilot thereofto view the terrain beneath the helicopter when it is airborne, andlaser alignment means for indicating when said helicopter is positionedvertically over a point on the terrain whose location it is desired tofix by survey, said laser alignment means including a laser capable ofprojecting a laser beam directed vertically between said helicopter andsaid point, a laser detector for detecting the laser beam, one of saidlaser and said laser detector being mounted on said helicopter, meansfor indicating to the pilot when the laser beam is aligned with saidlaser detector, and a distance measuring apparatus associated with saidhelicopter capable of determining the distance between the helicopterand said point.
 2. Target positioning apparatus as defined in claim 1wherein said laser detector is mounted on said helicopter, and furthercomprising electric circuit means connected to said laser detector forproviding an output signal in response to alignment of the laser beamwith said laser detector, said distance measuring apparatus comprisinghorizontal distance measuring apparatus operable in response to theoutput signal of said electric circuit means.
 3. Target positioningapparatus as claimed in claim 2, wherein said laser detector comprisesfirst and second laser sensing cell means responsive to said laser beamfor providing first and second signals, respectively, controlling saidelectric circuit means, said electric circuit means including means forinitiating and discontinuing operation of said distance measuring devicein response to said first and second signals, respectively.
 4. Targetpositioning apparatus as claimed in claim 1, wherein said laser detectoris mounted on said helicopter, and further comprising electric circuitmeans connected to said laser detector for providing an output signal inresponse to alignment of the laser beam with said laser detector, saiddistance measuring device comprising a height measuring device operablein response To said output signal for measuring the distance of saidhelicopter above said point.
 5. Target positioning apparatus as claimedin claim 4, wherein said laser detector comprises first and second lasersensing cell means responsive to said laser beam for providing first andsecond signals, respectively, controlling said electric circuit means,said electric circuit means including means for initiating anddiscontinuing operation of said distance measuring device in response tosaid first and second signals, respectively.
 6. Target positioningapparatus as claimed in claim 2, wherein said distance measuringaparatus comprises a height measuring device for measuring the distanceof said helicopter above said point.
 7. A method of surveying thelocation of a predetermined point on a terrain, which comprises thesteps of viewing the terrain below the helicopter and to facilitatemanoeuvering of the helicopter into a position generally above saidpoint, projecting a laser beam vertically between said helicopter andsaid point, positioning said helicopter accurately over said point byreference to said laser beam, and taking survey measurements while saidhelicopter is accurately positioned over said point.
 8. A method asdefined in claim 7 wherein said laser beam is projected verticallydownward from said helicopter, and said helicopter is positionedaccurately over said point by observation of the location of said beamrelative to said point.
 9. A method as defined in claim 7, whichincludes initiating the operation of distance measuring equipmentassociated with said helicopter in response to a signal generated by alaser detector on said helicopter indicating that the helicopter isaccurately positioned over said point.
 10. A method as claimed in claim9, which includes subsequently discontinuing operation of the distancemeasuring equipment by using said laser detector to sense when saidhelicopter has moved from over said point.